VBA calls C/C ++ DLL

 

In the development of VBA, in order to be able to use functions provided by the system or functions developed in C ++, This article summarizes the call of C ++ DLL by VBA.

 

1. function declaration

 

Function prototype:

 

Dword winapi GetCurrentDirectory (

 

_ In DWORD nBufferLength,

 

_ Out LPTSTR lpBuffer

 

);

 

The function declaration is as follows:

 

Public Declare Function GetCurrentDirectoryLib "kernel32" Alias "GetCurrentDirectoryA" (ByValnBufferLength As Long, ByVal lpBuffer As String) As Long

 

Public is used to declare functions that can be used for all other procedures in all modules. Private is used to declare functions that can only be used in modules that contain the declaration.

 

Lib contains the dynamic link library name or code Resource Name of the declared function.

 

Alias indicates that the called function has another name in the dynamic link library (DLL.

 

 

 

2. DLL location

 

The DLL file must be in one of the following three directories:

 

(1) Windows System directory: \ Windows \ system32

 

(2) Any directory indicated by path in DOS

 

(3) in Windows XP: C: \ Documentsand Settings \ % USERNAME % \ My Documents ents

 

In order for VBA to call functions in the DLL, The DLL must be placed in any of the above three positions.

 

There are two ways to solve this problem:

 

1. copy the DLL to any of the preceding three directories before calling the DLL function.

 

Dim fso AsObject

 

Dim dllFileNameAs String

 

DllFileName = Environ ("SYSTEMROOT") + "\ system32 \ LicenseVerify. dll"

 

Set fso = CreateObject ("Scripting. FileSystemObject ")

 

Iffso. FileExists (dllFileName) = False Then

 

Fso. CopyFile ThisWorkbook. Path + "\ LicenseVerify. dll", dllFileName

 

End If

 

 

 

2. Change the current path of the current process.

 

For example, if the DLL and the current EXCEL file are placed in the same directory, the current path of the current process is set as follows:

 

Public Declare Function SetCurrentDirectoryLib "kernel32" Alias "SetCurrentDirectoryA" (ByVallpPathName As String) As Long 'function declaration

 

SetCurrentDirectory (ThisWorkbook. Path) 'set the current directory to Thisworkbook. Path

 

OK. After this setting, you can access the DLL. In this way, you do not need to copy the DLL to the system directory to facilitate program release.

 

 

 

3. Return Value

 

If the returned value is a string, you need to allocate memory space for the string before calling the function.

 

Public Declare Function GetCurrentDirectoryLib "kernel32" Alias "GetCurrentDirectoryA" (ByValnBufferLength As Long, ByVal lpBuffer As String) As Long

 

LpBuffer is the output parameter.

 

Example:

 

Public Declare Function GetCurrentDirectoryLib "kernel32" Alias "GetCurrentDirectoryA" (ByValnBufferLength As Long, ByVal lpBuffer As String) As Long

 

 

 

Private Sub DoVerify ()

 

Dimresult As Integer

 

Dim retValue AsString

 

 

 

RetValue = String (1024, vbNullChar) 'allocate the buffer for out parameter.

 

 

Result = GetCurrentDirectory (1024, retValue)

 

End Sub